The present invention relates to shipbuilding and vessel repair, and more particularly, the present invention relates to a rebuilt double hull vessel and improved systems and methods for internally rebuilding a vessel having an existing single hull into a vessel having a double hull. Even more particularly, the present invention relates to improved systems and methods of internally fitting and attaching the new inner hull structure to the existing outer hull structure to form the rebuilt double hull vessel.
The shipping and cargo moving industry is continually faced with customer demands for new and improved vessel designs and for new and improved methods of modifying the design of existing vessels. Substantial cost savings can be realized by a vessel owner in modifying or rebuilding existing vessels to incorporate improvements in vessel designs or otherwise extend the life of the vessel rather than paying the cost of building a new vessel.
In addition, new governmental and environmental regulations place certain restrictions and requirements on vessel owners and operators. These new or required designs must be capable of securely holding a cargo and also of being seaworthy. At the same time, a vessel must comply with shipping and environmental requirements and regulations.
A typical vessel comprises a vessel having a single hull design. This type of hull construction provides a single outer hull or skin that provides structural integrity and acts as a boundary between the operating environment of the vessel (e.g., the sea) and the cargo and internal structure of the vessel. The single hull typically includes a shell having a bottom, a port side, a starboard side, a bow, a stem, a plurality of transverse and longitudinal bulkheads, and internal frames that support and strengthen the shell of the hull. This internal framing typically includes a combination of transverse and longitudinal members.
As a result of the recent heightened environmental awareness and several shipping mishaps, new governmental regulations have been implemented requiring the use of double hulls on designated vessels in U.S. waters out to the 200 mile economic zone limit. These double hull requirements are contained in the Oil Pollution Act of 1990 (OPA-90) and have been incorporated in U.S. Coast Guard regulations. In part, OPA-90 requires that all new tank vessels constructed under contracts awarded after 1990 must have double hulls and that all existing single hull vessels engaged in the marine transport of oil and petroleum products be rebuilt with double hulls or be retired between the years 1995 and 2015, depending on the size and age of the vessel.
This has created a great burden on carriers having existing single hull vessels. These single hull vessels will either have to be rebuilt to incorporate a double hull design at great cost to the carrier, or the vessel will have to be retired, in many cases years before the end of its economically useful life.
Double hull designs have been used in the construction of newer vessels in an effort to comply with the requirements of the OPA-90. These new construction, double hull vessels typically have an outer hull and an inner hull. The outer hull and the inner hull each have shell plating that forms the structural integrity of the hull. A combination of transverse and longitudinal framing is provided between the inner and the outer hull to help strengthen the shell plating. The idea behind a double hull is that the structural integrity of the outer hull may be breached without breaching the inner hull. Therefore, the outer hull may be breached, i.e., opened to the sea, while the cargo would remain securely contained within the inner hull. Thereby, a potential cargo spill will have been avoided. Typical cargos that have spilled in the past to cause environmental mishaps include cargos such as an oil, a petroleum, a chemical, or other hazardous materials. Of course the provision of a double hull adds to the complexity and cost of new construction.
Due to deviations in dimensions and equipment lay-out between the existing in-service vessel and the as-built vessel when it was new, difficulties exist with internally fitting the new inner hull over the existing outer hull to form the double hull vessel. Therefore a need exists for improved fit-up techniques for fitting the new inner hull to the existing outer hull in order to form the rebuilt vessel having a double hull.
The present invention is directed to a double hull vessel (particularly a sea going vessel) and improved systems and methods of internally rebuilding an existing vessel having a single hull design into a vessel having a double hull design. The present invention accomplishes the installation of the new double hull using an internal rebuild concept. The present invention reuses the existing vessel structure to the maximum extent possible, while also maintaining, as much as possible, the cargo carrying and hull operational characteristics of the original vessel. The shape and dimensions of the outer hull of the vessel and the hull performance characteristics of the vessel remain substantially the same, and the existing internal ship structure, including the longitudinal bulkheads, the transverse bulkheads, and top side decking are removed, modified, and reused to the maximum extent possible.
The outer hull of the existing single hull vessel and a new inner hull, which is disposed within a volume defined by the outer hull, define the double hull of the rebuilt vessel. A plurality of framing members are disposed between the inner hull structure and the outer hull and maintain the inner hull in a spaced apart relationship with the outer hull. The new inner hull defines an interior cargo carrying volume and the outer hull defines an exterior of the rebuilt vessel, such that the inner hull provides a boundary in the event that the outer hull is penetrated.
Preferably, the new inner hull structure which forms the new inner hull of the double hull vessel is prefabricated as a plurality of modular sections, and the prefabricated modules are fitted over the top of the existing bottom framing members and joined to the existing framing members at the sides. The prefabricated modules comprise portions of the inner hull plating including the inner bottom plating, port side plating, and starboard side plating, and a plurality of framing members. The framing members include stiffening members and connecting members. In one preferred embodiment, the connecting members include a plurality of transverse framing members and the stiffening members include a plurality of longitudinal framing members. Alternatively, the connecting members may include a plurality of longitudinal framing members and the stiffening members may include a plurality of transverse framing members. The connecting members are connected at one end to an exterior surface of the inner hull structure and extending therefrom and are connected at the other end to the outer hull structure.
The new portions of the primary framing members of the modular sections extend from the inner bottom plating a shorter distance than the new portions of the connecting members, thereby forming a gap when the module is installed over the existing framing. This gap helps facilitate fitting up and welding of each modular section to the existing outer hull structure. The removed internal ship structure and topside deck is modified and then reinstalled over the new inner hull after the inner hull has been installed. Thus, the cargo is primarily contained by new steel (the inner hull), and the exterior structure and coating of the original vessel""s hull define the outer hull of the vessel.
Accordingly, a single hull vessel is rebuilt to have a double hull over at least the entire side and bottom within the length of the cargo carrying volume, while substantially maintaining the major outer hull exterior dimensions and hull hydrodynamic characteristics of the original single hull vessel.
In accordance with a further aspect of the present invention, an improved connecting member and the use of advanced, computerized drafting and design techniques to improve the fit-up and connection of the new inner hull structure to the existing outer hull structure. More specifically, the improvements include: (a) using a face bar and filler plate combination to account for deviations in the hull structure thereby providing improved fit-up of the new inner hull structure to the existing outer hull structure; (b) performing a detailed vessel survey including measurement of various structural dimensions and accounting for deviations between as-built and existing structures including: the longitudinal distance between transverse frames and transverse bulkheads (e.g., the double bottom web of the new inner bottom and the bottom web of the existing structure) and the vertical gap between the new inner hull structure and the existing outer hull structure (e.g., the distance between the bottom of the face bar of the new hull and the top of the flange plate of the existing hull structure); (c) using Automated Computer-Aided Drafting (AUTOCAD) to ensure that the new and the existing structures come together smoothly by using graphical techniques to depict with a very high degree of accuracy the structure of the existing vessel and then tailoring the fabrication of the new inner hull structure to match the existing outer hull structure; and (d) using Finite Element Analysis (FEA) for evaluation of special structural details for best fit of new-to-existing structure ensuring acceptable stresses and long-term trouble-free service.
A double hull vessel rebuilt from an existing single hull vessel using the improved fit-up techniques includes an inner hull disposed within a volume defined by the existing outer hull so as to define a double hull. A plurality of framing members are disposed between the inner hull and the outer hull, including connecting members that maintain the inner hull in a spaced apart relationship with the outer hull. The connecting members include an inner connecting member and an outer connecting member that extend from the new inner hull the existing outer hull, respectively. A face bar and a filler plate are disposed between and connect the inner connecting member and the outer connecting member. The new inner hull defines an interior cargo carrying volume and the outer hull defines an exterior of the rebuilt vessel, such that the inner hull provides a boundary in the event that the outer hull is penetrated.
Preferably, the face bar is connected to a distal end of the inner connecting member on the new inner connecting member and the filler plate is connected to the face bar and a top portion of the outer connecting member.
The improved fit-up technique includes a fit-up tolerances that provides for an improved fit-up of the new inner hull to the existing outer hull by allowing a misalignment between the new inner connecting member and the existing outer hull connecting member. The fit up tolerances include a transverse fit up area defining an acceptable transverse offset between the new inner hull connecting member and the existing outer hull connecting member, and a vertical fit up area defining an acceptable vertical offset between the distal end of the inner connecting member and the top end of the existing outer hull connecting member.
Preferably, the fit up tolerances are determined based on the particular application and factors such as the type and size of the materials used to for the connection. Tolerance angles a are formed between an imaginary line extending from each comer of the distal end of the inner connecting member and help to determine the fit-up tolerances.
In one preferred embodiment, wherein the inner connecting member and the outer connecting member have a plate thickness of about xc2xd inch, the face bar has a plate thickness of about 1 inch, and the filler plate has a plate thickness of about xc2xd inch; the tolerance angles preferably include angles of about 45 degrees. This results in a transverse fit up area for the filler plate of about 2 {fraction (9/16)} inch for the transverse offset between the new inner hull connecting member and the existing outer hull connecting member and a vertical fit up area for the filler plate of about 2 {fraction (3/16)} inch for the vertical offset between the new inner hull connecting member and the existing outer hull connecting member.
The present invention is also directed to an improved method of fitting the new structure to the existing structure during the internal double hulling wherein the outer hull of an existing vessel is rebuilt internally using improved fit-up techniques to form a double hull. The method of double hull rebuild includes the steps of cutting an internal structure of the existing single hull vessel proximate an inner perimeter of the outer shell plating and an outer perimeter of the deck plating at least along a length of the cargo section; removing the cut internal structure from the outer shell plating; internally installing a new inner hull structure in a spaced apart relationship within a volume defined by the outer shell plating of the existing single hull vessel to form a double hull; connecting the inner hull structure to the existing outer hull structure using a face bar and a filler plate combination that account for deviations between the inner hull structure and the outer hull structure thereby providing improved fit up of the new inner hull structure to the existing hull structure; adapting the removed internal structure for reinsertion into the double hull; and reinstalling the adapted internal structure over an interior surface of the inner hull.
In accordance with one embodiment, the method further includes the steps of performing a detailed vessel survey including measuring the actual structural dimensions. The actual structural dimensions include, for example, the longitudinal distances between transverse frames and transverse bulkheads and the vertical gaps between the new inner hull structure and the existing outer hull structure.
The method can further includes the steps of using Automated Computer-Aided Drafting (AUTOCAD) to ensure that the new inner hull structure and the existing outer hull structure come together smoothly; using graphical techniques to depict with a very high degree of accuracy the outer hull structure of the existing vessel; and fabricating the new inner hull structure to match the existing outer hull structure. Finite Element Analysis (FEA) may be used for evaluation of special structural details for best fit of new-to-existing structure ensuring acceptable stresses and long-term trouble-free service.
Additional features of the present invention are set forth below.